Mutzl, J. ; Lenz, O. K. ; Landmann, G. ; Hinderer, Matthias (2018)
Palynology and micropalaeontology of Holocene lacustrine sediments of the Layla Lakes, central Saudi Arabia: Implications for changes of palaeoenvironment and palaeoclimate.
10th European Palaeobotany & Palynology Conference. Dublin (12.08.-17.08.18)
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Kurzbeschreibung (Abstract)

The Layla Lakes in central Saudi Arabia, located 300 km south of Riyadh, are fed by groundwater, but dried up in the late 1980’s due to extensive groundwater use, revealing a series of 23 sinkholes in the Jurassic Hith formation. In one of them with a size of 400 x 100 m and a depth of 10 m several samples were taken during a field campaign in 2011. Furthermore a sediment core was drilled near the sinkhole, revealing a lacustrine succession of 10.8 m. Mineralogical and geochemical analyzes show two distinct types of sedimentation: Sediments with an average content of 85% calcite (carbonates) and sediments, which consist almost entirely of gypsum and anhydrite (sulfates).

The carbonates precipitated when the exchange between groundwater and lake water was too large to achieve supersaturation of gypsum, while the sulfates mark periods of strong evaporation with limited rates of water exchange. First radiocarbon ages of mollusc shells and U/Th dating of carbonates indicate that the sedimentary succession covers 6000 years. Autochthonous microfossil assemblages comprise pollen, spores, diatoms, freshwater algae, testate amoebae, phytoliths and other non-pollen palynomorphs as well as zoological remains and offer the application of various multi-proxy methods to reconstruct Holocene palaeoclimate and palaeoenvironment in the center of Saudi Arabia in detail, a region, where such a complete sedimentary record is unknown so far.

Our study shows that the shore lines of the Layla Lakes were covered by a dense herbaceous vegetation during humid times. The environment was characterized by grasslands, interspersed with Chenopodiaceae. Wet places at the lake shore were vegetated by ferns. At peak periods of humid climate even water lilies, cattails and Ceratophyllaceae (hornworts) existed, which were spread on the lake water surface or grew completely submerged. During dry phases the lake level decreased significantly and the vegetation was replaced by plants that were adapted to arid conditions. A first semiquantitative analysis of the samples reveals distinct frequency fluctuations in various microfossil groups, which indicate cyclic climate variations between dry and more humid phases on a millennial scale. XRF and visual analyses of sediment composition confirm at least four changes between arid and more humid phases based on the frequency of carbonate and sulfate sediments.

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